This invention relates generally to vibration sensing, and specifically to sensing musical drumhead vibrations using an ultrasonic transducing element.
This invention comprises a device that permits sensing of surface vibrations by use of reflected sound at a frequency substantially higher than that of the surface vibrations to be sensed. One important application is for sensing drumhead vibrations of a tunable drum so as to provide a signal to a sound analyzer that displays to the drum""s player the note that is being played and the accuracy of its pitch relative to the standard musical scale.
Present sensing devices for this purpose utilize electromagnetic, optical, or acoustic methods that operate without contacting the drumhead, or piezoelectric or other methods that require the sensing element to be in physical contact with the drumhead. Each of these methods has its deficiencies insofar as pickup of extraneous signals such as xe2x80x9cAC humxe2x80x9d (from electrical environment or from the room lighting) or room ambient sound, requiring use of a separate xe2x80x9ctargetxe2x80x9d that must be attached to the drumhead, direct contact with the drum head, and/or difficult setup and calibration/alignment.
Ultrasonic transducing elements are used to measure vibrations of a nearby musical drumhead or other vibrating surface. A first ultrasonic transducer emits an ultrasonic signal and a second ultrasonic transducer listens for an echo of that signal. A phase change of the echoed (reflected) signal is compared to a reference signal to create a representation signal which represents the movement of the drumhead or other vibrating surface. For this comparison to be properly made, a deviation signal is generated that defines an average deviation of the reference signal from optimum, which is then used to self-align the reference signal to the reflected signal.
The disclosed invention is capable of operating at a relatively large distance from the drumhead. It does not contact the drumhead nor does it require a special target to be placed on the drumhead. It does not require any specialized setup, does not contact the drumhead, and is insensitive to interference from room ambient sound, electromagnetic signals, lighting/optical signals, or temperature changes. All of these are significant advantages relative to presently-used vibration sensing methods. Ease of installation is another major advantage. To use the sensor, it is simply fixtured in place with its active elements facing the drumhead. Within a large operating range, the sensor system automatically compensates (self-aligns) for differences in the set operating distance to the drum head, air temperature, and other variables.